1. Field of the Invention
The invention relates to a photosensitive resin composition, more particularly to a photosensitive resin composition for forming a protective film having a good cross-sectional shape and a low linear thermal expansion coefficient. This invention also relates to a protective film formed from the photosensitive resin composition, and an element containing the protective film.
2. Description of the Related Art
While manufacturing an optical device such as a liquid crystal display or a solid state imaging device, processing procedures such as soaking in acid or alkaline solutions and sputtering, and heat generated during the processing procedures may damage the optical device. Therefore, a protective film is usually needed for protecting the optical device.
The protective film is not only required to have superior resistance to chemicals, water, and solvents so as to provide sufficient protection against the aforementioned conditions, but also to have good adhesion to a substrate, high transparency and good thermal and light resistances so as to prevent whitening or yellowing problems after being used for a long period of time.
JP 2001-354822 discloses a radiation-sensitive resin composition which includes: (A) a copolymer of an unsaturated carboxylic acid and/or an unsaturated carboxylic acid anhydride, an epoxy-containing unsaturated compound, a maleimide monomer, and other olefinic unsaturated compound; and (B) 1,2-quinonediazide compound, wherein the amount of the 1,2-quinonediazide compound (B) ranges from 5 to 100 parts by weight based on 100 parts by weight of the copolymer (A). Such radiation-sensitive resin composition has good sensitivity and the protective film formed therefrom has good thermal and solvent resistances. However, the protective film has relatively high linear thermal expansion coefficient and inferior cross-sectional shape, thereby adversely affecting accuracy of the following process such as forming a wiring electrode layer on the protective film.
Therefore, there is a need in the art to provide a protective film that has a good cross-sectional shape and a low linear thermal expansion coefficient.